1. Field of the Invention
The present invention relates generally to the field of bridge construction and maintenance and, more specifically to apparatus for assembling flexible expansion joint systems of the type generally termed "strip seals" in bridges.
2. Description of the Prior Art
Bridges, designed to carry vehicular traffic, often include a plurality of adjacent, prestressed, concrete slabs which present a road or deck surface. The slabs are usually supported by steel beams resting on concrete pillars or abutments.
Because bridges are subjected to a wide range of temperatures, the concrete slabs are separated by a narrow gap or expansion joint which permits them to expand and contract freely. Often the expansion joint is fitted with a tough and resilient seal so that a continuous, water tight road surface is formed. This helps to prevent the corrosive effects of precipitation and road salt from reaching the underlying support structure.
The size of the expansion joint left between the concrete slabs during bridge construction varies with the length of the slab and the ambient temperature at the time the slab is poured. The object, of course, is to provide at least some clearance between the slabs when the ambient temperature is high and to minimize the clearance and the resulting discontinuity in the road surface when the ambient temperature is low.
It will be recognized by those skilled in the art of bridges construction, that the term "expansion joint" is often used to designate the above-mentioned gap between concrete slabs as well as the resilient sealing material fitted into the gap. As used herein, the term "expansion joint" shall refer only to the aforementioned gap and the term "expansion joint system" shall be used to refer to the resilient sealing material and associated anchoring apparatus.
Currently, expansion joint system of the type generally referred to as "strip seals" are being widely used in bridge construction in the U.S. and Canada. These types of expansion joint systems generally include a pair of rigid rails having a flexible strip seal, called a seal gland, disposed therebetween. Usually, the rails are fabricated from extruded or roll-formed steel and the seal gland from a tough, resilient material such as neoprene. The rails are laid generally transverse to the longitudinal direction of the bridge, one rail of each pair being anchored to each edge of adjacent concrete slabs. The seal gland is affixed to each rail by means of an interlocking seam, the formation of which is made possible by the geometry of the seal gland and rails, as explained below.
The seal gland has a substantially uniform transverse cross sectional configuration and comprises a strip-like flexible seal web with a compressible head section formed along each of the web's longitudinal edges. The compressible head sections generally have dimensions larger than the thickness of the web material so that each head section presents a pair of shoulders that run the length of the seal gland. The transverse cross section of the web defines one or more accordian-like pleats which run parallel to the longitudinal axis of the web so that the web is capable of being folded on itself. Usually, the web includes only a few pleats so that when in place, the configuration is a V-shaped or W-shaped trough.
Each rail also has a substantially uniform transverse cross sectional configuration which delineates an involute channel that runs the length of the rail. The involute channel includes a relatively narrow throat section and a relatively bulbous interior and is adapted for receiving one of the compressible head sections of the seal gland. Thus, the transverse cross sectional configuration of each rail in the pair is substantially a mirror image of its counterpart.
After the rails have been anchored in place along the edges of adjacent concrete slabs, the seal gland is laid between the rails with the compressible head sections adjacent the involute channels of the rails. Generally, the lowermost shoulder on each compressible head is inserted through the restricted throat of the involute channel so that the seal gland rests on the rails. The uppermost shoulder is then forced to squeeze through the throat and into the bulbous interior of the adjacent involute channel. To accomplish this the compressible head collapses and then expands to its unstressed shape completely filling the throat. The shoulders presented by the compressible heads are of a dimension slightly larger than the throat so that an interlocking seam is formed between the rail and seal gland. The flexible seal web is folded on its pleats to form the aforementioned V-shaped or W-shaped trough which assumes an angle that is dependent on the distance separating the rails.
Heretofore one of the most difficult steps in assembling a flexible strip seal expansion joint system has been the last, that is forcing the uppermost shoulder of the compressible head through the throat of the involute channel in the rail. This has generally been accomplished in a sequential manner on short sections of the seal gland. A pry bar is engaged with the uppermost shoulder and the tool along with the head are forced through the throat. Often times removal of the pry bar also results in removal of the shoulder or the entire compressible head from the involute channel.
Attempts have been made to reduce the frictional forces exerted on the compressible head by lubrication of the head or the involute channel prior to installation. Often times a liquid epoxy adhesive is employed which serves to initially lubricate the head and later to further anchor the installed seal gland.
Even with lubricants, installations of the seal gland using the above-described prior art method is very labor intensive. It is estimated that a four man crew can install only about 140 linear feet of a seal gland per day. This is the equivalent of 35 linear feet per man-day.
The present invention overcomes the drawbacks of the prior art method and tools for installing seal glands in flexible expansion joint systems. The seam forming apparatus of the present invention permits the installation of approximately 340 feet of seal gland per 8 hour day by a two man crew. This is the equivalent of 170 linear feet per man day.